System for station group management and method for managing station-management groups

ABSTRACT

Embodiments of a system for station group management and a method for managing station-management groups in a wireless network are generally described herein. In some embodiments, a system element, such as an access point, may establish a station-management group including selected stations, transmit a unicast group allocation message to a station to indicate whether the station is part of the station management group, transmit data frames to the station in a downlink (DL) multi-user multiple-input multiple-output (MU-MIMO) transmission, and delete the station from the station-management group.

This application is a continuation of U.S. patent application Ser. No.13/461,909, filed on May 2, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/842,239, filed on Jul. 23, 2010, now issued asU.S. Pat. No. 8,194,687, each of which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

Embodiments pertain to wireless communications includingwireless-fidelity (WiFi) communications. Some embodiments relate tomulti-user multiple-input multiple-output (MU-MIMO) communications. Someembodiments pertain to MU-MIMO systems that use a downlinkspace-division multiple access (DL-SDMA) technique. Some embodimentspertain to MU-MIMO systems that operate in accordance with one of theIEEE 802.11 standards, such as the 802.11ac standard.

BACKGROUND

MU-MIMO systems use multiple spatial channels to transmit and receivesignals to/from multiple stations at the same time using two or moreantennas. In a MU-MIMO system, the signals for the different stationsare precoded for transmission on different spatial channels, allowingthe stations to separate out the data intended for a particular station.One issue with MU-MIMO systems is managing and maintaining groups ofstations.

Thus there are general needs for access points configured for stationgroup management and methods for managing station-management groups.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a basic service set (BSS) in accordance with someembodiments;

FIG. 2A illustrates the frame format of a group allocation messageconfigured for explicit deletion of station-management groups inaccordance with some embodiments;

FIG. 2B illustrates the frame format of a group deletion message inaccordance with some embodiments;

FIG. 2C illustrates a DL MU-MIMO transmission in accordance with someembodiments;

FIG. 3 is a state diagram for an access point configured for explicitdeletion of station-management groups in accordance with someembodiments;

FIG. 4 is a state diagram for a station configured for explicit deletionof station-management groups in accordance with some embodiments;

FIG. 5 illustrates the frame format of a group allocation messageconfigured for implicit deletion of station-management groups inaccordance with some embodiments;

FIG. 6 is a state diagram for an access point configured for implicitdeletion of station-management groups in accordance with someembodiments; and

FIG. 7 is a state diagram for a station configured for implicit deletionof station-management groups in accordance with some embodiments.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

FIG. 1 illustrates a basic service set (BSS) in accordance with someembodiments. BSS 100 includes an access point (AP) 102 and a pluralityof associated communication stations (STA) 104. In accordance withembodiments, the access point 102 is configured to transmit data framesto the stations 104 that are part of a station-management group using aMU-MIMO technique. As described in more detail below, the access point102 may establish, maintain and delete one or more station-managementgroups, such as station-management group 105 and station-managementgroup 115, within the BSS 100. Stations 104 may also maintainnon-interfering peer link groups with peer-to-peer links 107.

As illustrated in FIG. 1, the access point 102 is configured to transmitdata frames 103 to the stations 104 that are part of station-managementgroup 105 using a MU-MIMO technique. The access point 102 may also beconfigured to transmit data frames 113 to the stations 104 that are partof station-management group 115 using a MU-MIMO technique. Data frames103 transmitted to the stations 104 of the station-management group 105,and data frames 113 transmitted to the stations 104 of thestation-management group 115 may be referred to as downlink (DL) MU-MIMOtransmissions, which are described in more detail below.

In accordance with embodiments, the access point 102 may select stations104 for a station-management group 105 and transmit a group allocationmessage to the selected stations 104. The access point 102 may alsoestablish a station-management group 105 that includes stations 104 fromwhich response frames were received. A response frame may be anacknowledge (ACK) frame or a frame that includes channel-stateinformation (CSI) feedback. While the station-management group 105 isestablished, the access point 102 may transmit data frames 103 to thestations 104 of the station-management group 105 using a MU-MIMOtechnique.

The access point 102 may also either explicitly delete a station 104from the station-management group 105 by transmitting a group deletionmessage to the station 104, or implicitly delete a station 104 from thestation-management group 105 by refraining from transmitting DL MU-MIMOtransmissions or group update messages to the station 104. Theseembodiments are described in more detail below.

The access point 102 and the stations 104 of BSS 100 may implement acarrier-sense multiple access technique (CSMA) for accessing thewireless medium, such as the carrier-sense multiple access withcollision avoidance (CSMA/CA) technique of IEEE 802.11. The access point102 and the stations 104 may also implement a MU-MIMO technique of IEEE802.11ac.

The access point 102 and stations 104 may include several separatefunctional elements to implement the operations described herein,including a radio transceiver, processing circuitry and memory. One ormore of the functional elements may be combined and may be implementedby combinations of software-configured elements, such as processingelements including digital signal processors (DSPs), and/or otherhardware elements. For example, some elements may comprise one or moremicroprocessors, DSPs, application specific integrated circuits (ASICs),radio-frequency integrated circuits (RFICs) and combinations of varioushardware and logic circuitry for performing at least the functionsdescribed herein.

In some embodiments, stations 104 may be a fixed or mobile wirelesscommunication device, such a personal digital assistant (PDA), a laptopor portable computer with wireless communication capability, a smartphone, a web tablet, a wireless telephone, a wireless headset, a pager,an instant messaging device, a digital camera, an access point, atelevision, a medical device (e.g., a heart rate monitor, a bloodpressure monitor, etc.), or other device that may receive and/ortransmit information wirelessly.

FIG. 2A illustrates the frame format of a group allocation messageconfigured for explicit deletion of station-management groups inaccordance with some embodiments. The group allocation message 202 maybe transmitted by the access point 102 (FIG. 1) to indicate to which ofstations 104 (FIG. 1) are selected to be part of a station-managementgroup 105 (FIG. 1). The numbers above each field of the group allocationmessage 202 may indicate the length of each of the fields in octets.

In accordance with embodiments, the group allocation message 202includes a group identification (ID) field 204 within the frame body toidentify the station-management group 105 and a plurality of associatedidentifier (AID) fields 206 to identify the associated IDs of thestations 104 that are being selected for the station-management group105. The group allocation message 202 may be transmitted in either abroadcast or a unicast fashion. When transmitted in a broadcast fashion,the receiver address (RA) of the group allocation message 202 is thebroadcast address.

The frame body of the group allocation message 202 may also include acategory field and an action field indicating that the message is agroup allocation message, and a length field indicating the length ofthe frame body.

FIG. 2B illustrates the frame format of a group deletion message inaccordance with some embodiments. The group deletion message 232 may betransmitted by an access point 102 (FIG. 1) to delete an establishedstation-management group 105 (FIG. 1) or to remove one or more stations104 (FIG. 1) from the established station-management group 105. Thenumbers above each field of the group allocation message 232 mayindicate the length of each of the fields in octets. When configured toremove one or more stations from a station-management group, the groupdeletion message 232 may be considered a station deletion message.

The group deletion message 232 may be addressed to the one or morestations 104 of the station-management group 105 that are to be deleted.The group deletion message 232 may include a group ID field 234 in theframe body to identify the station-management group 105. The groupdeletion message 232 may be addressed to the stations being removed fromthe group using the RA field.

The frame body of the group deletion message 232 may also include acategory field and an action field indicating that the message is agroup allocation message, and a length field indicating the length ofthe frame body.

FIG. 2C illustrates a DL MU MIMO transmission in accordance with someembodiments. The DL MU MIMO transmission 240 may be transmitted by anaccess point to stations that are part of an establishedstation-management group. The DL MU MIMO transmission 240 may correspondto data frames 103 (FIG. 1) that are transmitted in accordance with aMU-MIMO technique to station management group 105 (FIG. 1), or dataframes 113 (FIG. 1) that are transmitted in accordance with a MU-MIMOtechnique to station management group 115 (FIG. 1). The DL MU MIMOtransmission 240 may comprise a concurrent transmission ofspatially-separated data packets 250 to at least some of the stations104 of a station-management group.

As illustrated in FIG. 2C, the spatially-separated data packets 250 maycomprise a plurality of individual data packets, such as data packet251, data packet 252 and data packet 253, transmitted concurrentlywithin the same frequency spectrum. Data packet 251 may be intended fora first station (STA1), data packet 252 may be intended for a secondstation (STA2) and data packet 253 may be intended for a third station(STA3). Although individual data packets 251, 252, 253 are separatelyillustrated in FIG. 2C, this does not imply that they are transmitted onseparate frequency channels.

In some embodiments, each data packet 250 may be separately precoded forreceipt by the receiving stations. These embodiments are described inmore detail below.

The spatially-separated individual data packets 250 may be transmittedconcurrently on the same frequency channel, which may comprise the sameset of orthogonal frequency division multiplexed (OFDM) frequencysubcarriers. Each of the individual data packets 250 may be addressed toand precoded for receipt by one of the stations 104 of thestation-management group 105. In these embodiments, the individual datapackets may be transmitted at the same time and each data packet 250 maybe transmitted on a different spatial channel. In these embodiments, aDL MU MIMO or a DL SDMA technique may be employed.

In some embodiments, a single frequency channel may be used to transmitthe DL MU MIMO transmission 240. In some IEEE 802.11ac embodiments, aprimary frequency channel and up to seven secondary frequency channelsmay be used to transmit the DL MU-MIMO transmissions 240. Each frequencychannel may be a 20-MHZ frequency channel and may use a plurality ofOFDM subcarriers.

The plurality of individual data packets 250 of the DL MU-MIMOtransmission 240 may be transmitted as a single frame by the accesspoint 102 in accordance with a CSMA/CA technique. After transmission ofthe individual data packets 250, the access point 102 may receiveindividual acknowledgements 255, such as block acknowledgements (BA)255, from the stations 104 of the station-management group 105. Theacknowledgements 255 may be transmitted by the stations in accordancewith a CSMA/CA technique on the same frequency channel in response toreceipt of the DL MU-MIMO transmission 240. Although blockacknowledgements 255 are illustrated in FIG. 2C, this does not implythat they are transmitted on different frequency channels.

A DL MU-MIMO transmission 240 may be a single frame that may include,among other things, one or more training fields and one or moresignaling fields. A DL MU-MIMO transmission 240 may be configured inaccordance with an IEEE 802.11 standard.

FIG. 3 is a state diagram for an access point configured for explicitdeletion of station-management groups in accordance with someembodiments. An access point, such as access point 102 (FIG. 1), mayoperate in accordance with state diagram 300. During idle state 301, theaccess point 102 is idle with respect to station group managementactivities. After transmitting a group allocation message, such as groupallocation message 202 (FIG. 2A), to selected stations 104 (FIG. 1), theaccess point 102 may enter the group setup wait state 302. When responseframes are received from one or more of the selected stations 104, theaccess point 102 may establish a station-management group 105 to includestations 104 from which response frames are received and enter theestablished state 304. While in the established state 304, the accesspoint 102 may transmit a DL MU-MIMO transmission 240 to the stations 104of the established station-management group 105 using a MU-MIMOtechnique. While in the established state 304, the access point 102 mayexplicitly delete the station-management group 105 by transmitting agroup deletion message 232 (FIG. 2B) or a station deletion message andenter the deletion wait state 306. During the deletion wait state 306,the access point 102 may wait for stations to acknowledge receipt of thegroup deletion message 232. After all stations 104 are deleted from thestation-management group 105 or a retry limit is reached, the accesspoint 102 may return to the idle state 301.

As illustrated in state diagram 300, the access point 102 may return tothe idle state 301 from the group setup wait state 302 when no responseframes are received from any of the selected stations 104 within apredetermined period of time. The access point 102 may also retrysending a station deletion message while in the deletion wait state 306and return to the established state 304 if there is station remaining inthe group.

FIG. 4 is a state diagram for a station configured for explicit deletionof station-management groups in accordance with some embodiments. Acommunication station, such as one of communication stations 104 (FIG.1), may operate in accordance with state diagram 400. During idle state402, the communication station 104 may receive a group allocationmessage 202 (FIG. 2A) from an access point 102 (FIG. 1) and enter groupsetup wait state 404. In response to the group allocation message 202,the communication station 104 may send a response frame, such as an ACKframe or a frame that includes CSI feedback, to indicate that it willjoin a station-management group 105 (FIG. 1) indicated in the groupallocation message 202 and enter the established state 406. During theestablished state 406, the communication station 104 is a member of thestation-management group 105 and may receive DL MU-MIMO transmission 240(FIG. 2C) from the access point 102. In these explicit group deletionembodiments, the communication station 104 may remain in the establishedstate 406 until it receives a group deletion message from the accesspoint.

FIG. 5 illustrates the frame format of a group allocation messageconfigured for implicit deletion of station-management groups inaccordance with some embodiments. The group allocation message 502 maybe transmitted by the access point 102 (FIG. 1) to stations 104 (FIG. 1)that are selected to be part of a station-management group 105 (FIG. 1).The numbers above each field of the group allocation message 502 mayindicate the length of each of the fields in octets.

In accordance with embodiments, the group allocation message 502includes a group ID field 504 within the frame body to identify thestation-management group 105 and a plurality of AID fields 506 toidentify the associated IDs of the stations 104 that are being selectedfor the station-management group 105. The frame body of the groupallocation message 502 may also include a timeout field 514 to indicatea maximum duration of group membership. In these embodiments, the accesspoint 102 will automatically delete the station-management group when nogroup update messages or no DL MU-MIMO transmissions 240 are sent afterthe predetermined period of time indicated in timeout field 514 to thestations of the established station-management group 105. Theseembodiments are discussed in more detail below. In some embodiments,timeout field 514 may indicate a timeout interval in milliseconds.

The frame body of the group allocation message 502 may also include acategory field indicating that the message is a group allocation messageconfigured for implicit group deletion, an action field, and a lengthfield indicating the length of the frame body. Other fields may beincluded in the frame body of the group allocation message 502, groupallocation message 202 (FIG. 2A), and group deletion message 232 (FIG.2B).

In these embodiments, station-management groups may be established fortime periods ranging from 10 milliseconds to a much longer period suchas hours. The establishment and reestablishment of station-managementgroups in both the explicit group deletion and implicit group deletionembodiments allows an access point to dynamically update and changemembers of a station-management group based on, among other things,traffic patterns of the individual stations and changing channelconditions.

FIG. 6 is a state diagram for an access point configured for implicitdeletion of station-management groups in accordance with someembodiments. An access point, such as access point 102 (FIG. 1) mayoperate in accordance with state diagram 600. During idle state 601, theaccess point 102 is idle with respect to station group managementactivities. After transmitting a group allocation message, such as groupallocation message 502 (FIG. 5), to selected stations 104 (FIG. 1), theaccess point 102 may enter the group setup wait state 602. When responseframes are received from one or more of the selected stations 104, theaccess point 102 may establish the station-management group 105 toinclude stations 104 from which response frames are received and enterthe established state 604 and establish a station-management group 105(FIG. 1). While in the established state 604, the access point 102 maytransmit a DL MU-MIMO transmission 240 (FIG. 2C) to the stations 104 ofthe station-management group 105. While in the established state 604,the access point 102 may implicitly delete the station-management group105 by refraining from transmitting DL MU-MIMO transmissions 240 orgroup update messages to the stations 104 of the establishedstation-management group 105 after a predetermined period of timeindicated in timeout field 514 (FIG. 5) and return to idle state 601.While in the established state 604, the access point 102 may entermaintenance wait state 606 while waiting for acknowledgement frames orCSI feedback from stations 104 in response to a DL MU-MIMO transmission240. Data packets may be retransmitted when acknowledgements are notreceived in accordance with conventional techniques.

As illustrated in state diagram 600, the access point 102 may return tothe idle state 601 from the group setup wait state 602 when no responseframes are received from any of the selected stations 104 within apredetermined period of time. The access point 102 may also return tothe idle state 601 after a predetermined period of time after a retrylimit is reached for stations that do not respond with to the a DLMU-MIMO transmission 240.

FIG. 7 is a state diagram for a communication station configured forimplicit deletion of station-management groups in accordance with someembodiments. A communication station, such as one of communicationstations 104 (FIG. 1), may operate in accordance with state diagram 700.During idle state 702, the communication station 104 may receive a groupallocation message 502 (FIG. 5) from an access point 102 (FIG. 1) andenter group setup wait state 704. In response to the group allocationmessage 502, the communication station 104 may send a response frame,such as an ACK frame or a frame including CSI feedback , to indicatethat it will join the indicated station-management group and enter theestablished state 706. During the established state 706, thecommunication station 104 may receive DL MU-MIMO transmissions 240 (FIG.2C) from the access point 102. The communication station 104 may remainin the established state 706 until it no longer receives any DL MU-MIMOtransmissions 240 or group update messages for the predetermined periodof time indicated in timeout field 514 (FIG. 5) of the group allocationmessage 502.

Referring to FIGS. 1, 2A, 2B, 2C, and 5 as discussed above, the accesspoint 102 is configured to set up and manage one or morestation-management groups 105 by transmitting a group allocation messageto selected stations 104. Group allocation message 202 (FIG. 2A) may betransmitted when the access point 102 employs explicit group deletion,and group allocation message 502 (FIG. 5) may be transmitted when theaccess point 102 employs implicit group deletion. The access point 102may establish the station-management group 105 to include stations fromwhich response frames are received. The access point 102 may transmit DLMU-MIMO transmissions 240 to the stations of the station-managementgroup 105 using a MU-MIMO technique. The access point 102 may eitherexplicitly delete the station-management group by transmitting a groupdeletion message 232 to the stations of the group or implicitly deletethe station-management group by refraining from transmitting DL MU-MIMOtransmissions 240 or group update messages to the stations of the groupfor a predetermined period of time. In some embodiments, the accesspoint 102 may concurrently establish more than one station-managementgroup.

In some embodiments, the response frames are transmitted by at leastsome of the selected stations 104 in response to receipt of a groupallocation message 202 or 502, and the access point 102 establishes thestation-management group 105 to include stations 104 from which responseframes are received within a predetermined period of time. In theseembodiments, the response frames are acknowledge frames, and allstations that receive a group allocation message send back anacknowledge frame. Based on the receipt of acknowledge frames, theaccess point 102 may decide which of the stations to include in thestation management group.

In some embodiments, the access point 102 may attempt to establish astation-management group 105 within a predetermined period of time.During this period of time, the access point 102 may transmit one ormore group allocation messages to selected stations 104. Stations 104that respond within this period of time may become part of the indicatedstation-management group 105.

In some embodiments, the access point 102 may explicitly delete one ormore stations 104 from the established station-management group 105 bytransmitting a group deletion message 232 to one or more of the stations104 of the established station-management group 105. In someembodiments, the access point 102 may implicitly delete one or morestations 104 from an established station-management group 105 byrefraining from transmitting a DL MU-MIMO transmission 240 or groupupdate messages to one or more stations 104 for a predetermined periodof time. Stations 104 that are deleted from the station-management groupmay be deleted from a memory of the access point 102 that identifiesstations currently part of a station-management group.

When the access point 102 is configured for implicit group deletion, noexplicit messages need to be transmitted to the stations 104 of anestablished station-management group 105 to indicate that stations arebeing removed or the station-management group 105 is being deleted. Thestations of the station-management group 105 are automatically deletedas discussed above by refraining from transmitting DL MU-MIMOtransmissions 240 or group update messages for a predetermined period oftime.

When the access point 102 is configured for explicit deletion, stations104 may respond to the group deletion message 232 with anacknowledgement frame. These responding stations 104 may be deleted fromthe station-management group 105 after the acknowledgement frame isreceived by the access point 102.

As discussed above, a DL MU-MIMO transmission 240 may comprise aconcurrent transmission of spatially-separated data packets 250 to atleast some of the stations 104 of the station management group 105employing a DL MU MIMO or DL SDMA technique. In some embodiments,beamforming may be employed by the access point 102 as well as thestations 104 for transmitting and receiving. In some embodiments, astation-management group may be a DL SDMA group when an SDMA techniqueis used to transmit DL MU-MIMO transmissions 240.

In embodiments that employ DL-SDMA, the individual data packets 251,252, and 253 may be precoded based on a CSI matrix for the stations 104of the station-management group 105. In these embodiments, the precodingmatrix may be generated from the CSI for each station 104, and theprecoding matrix may be used to precode the individual data packets forconcurrent transmission within a DL MU-MIMO transmission 240. Thestations 104 include processing circuitry to separate their packet frompackets intended for other stations based on the station's CSI or theCSI matrix. In some of these embodiments, the group allocation message202 may be used as a sounding frame by the stations 104 to determinetheir CSI.

The access point 102 may be configured to select stations 104 for thestation-management group 105 based on the CSI of the stations 104associated with the access point within the BSS 100. Stations 104 havinga greatest difference between their CSI's may be selected for astation-management group 105, although this is not a requirement. Inthese embodiments, the greater difference in CSI's between stations 104of a station-management group 105 may provide for a greater spatialchannel separation by precoding, making it easier for a station 104 toseparate out its data packet from the other data packets within a DLMU-MIMO transmission 240. In some embodiments, based on interferingpatterns of different peer-to-peer links 107 between peer stations 104,the access point 102 may select stations 104 for differentstation-management groups 105 and 115 so that peer-to-peer links 107within a group can be used to communicate simultaneously without causinginterference to each other's directional transmissions. Although FIG. 1illustrates stations 104 of station-management group 105 being locatedtogether and stations of station-management group 115 being locatedtogether, this may not be the case when stations 104 are selected for astation-management group based on their CSI.

In some embodiments, when the access point 102 has buffered traffic fora station 104 after the station 104 is removed from a station-managementgroup 105 (either explicitly or implicitly), the access point 102 maytransmit the buffered traffic as unicast traffic to the station ratherthan transmitting the traffic as part of a DL MU-MIMO transmission 240.

In some embodiments, a station 104 may be removed from a group if thestation's CSI has changed (e.g., if the CSI of the station 104 is notsufficiently different from the CSI of other stations to allow forsufficient signal separation by precoding) or if there has been notraffic for the station 104.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

1. (canceled)
 2. An apparatus of an access point comprising hardwareprocessing circuitry and memory configured to: generate a group IDmanagement frame to establish group assignments for a multi-user (MU)multiple-input multiple-output (AMMO) (MU-MIMO) transmission, the groupID management frame comprising a membership status field and a userposition field, the membership status field indicating group membershipstatus of stations (STAs) for a plurality of group IDs, the userposition field indicating positions for the group IDs for STAsidentified as group members in the membership status field; andconfigure the MU-MIMO transmission for transmission to the stationsindicated as being members in one of the groups, the MU-MIMOtransmission comprising a group ID field indicating one of the group IDsand a multi-user field indicating a number of space-time streams for thestations associated with indicated group ID, wherein the space-timestreams for different stations are ordered based on the user positionfield of the group ID management frame.
 3. The apparatus of claim 2further configured to: establish a station-management group to includetwo or more selected stations; configure the group ID management frameto identify the selected stations in the membership status field.
 4. Theapparatus of claim 3 further configured to generate a group updatemessage comprising a group ID management frame to inform a station ofits explicit deletion from the station-management group.
 5. Theapparatus of claim 4 further configured to implicitly delete a stationfrom the station-management group by refraining, for a predeterminedperiod of time, from transmission of MU-MIMO transmissions or groupupdate messages to the station to inform the station of its implicitdeletion from the station-management group.
 6. The apparatus of claim 3,further configured to decode an acknowledgment (ACK) frame or channelstate information (CSI) from a station of the station management groupin response to receipt the group ID management frame by the station. 7.The apparatus of claim 3, wherein the MU MIMO transmission is atransmission in accordance with a channel-sense multiple-access withcollision avoidance (CSMA/CA) technique, and wherein the access point isconfigured to receive individual acknowledgements from the stations ofthe station-management group, the acknowledgements having beentransmitted by the stations in accordance with a CSMA/CA technique. 8.The apparatus of claim 3 further comprising transceiver circuitryconfigured to precode individual data packets of the MU MIMOtransmission based on channel state information (CSI) for each of thestations of the station-management group indicated by the group IDfield.
 9. The apparatus of claim 3 wherein the access point isconfigured to operate as part of a basic-service set (BSS) in accordancewith an IEEE 802.11 standard, wherein the access point is configured toselect stations from the BSS for the station-management group.
 10. Theapparatus of claim 9, wherein the access point is configured to selectstations from the BSS for the station-management group based on channelstate information (CSI) and/or traffic patterns.
 11. The apparatus ofclaim 9, wherein the access point is configured to select stations fromthe BSS for a station-management group having channels with lowerchannel correlation, wherein stations having higher channel correlationsare selected for different station-management groups.
 12. Anon-transitory computer-readable storage medium that stores instructionsfor execution by one or more processors of an access point (AP) toconfigure the AP to perform operations to: generate a group IDmanagement frame to establish group assignments for a multi-user (MU)multiple-input multiple-output (MIMO) (MU-MIMO) transmission, the groupID management frame comprising a membership status field and a userposition field, the membership status field indicating group membershipstatus of stations (STAs) for a plurality of group IDs, the userposition field indicating positions for the group IDs for STAsidentified as group members in the membership status field; andconfigure the MU-MIMO transmission for transmission to the stationsindicated as being members in one of the groups, the MU-MIMOtransmission comprising a group ID field indicating one of the group IDsand a multi-user field indicating a number of space-time streams for thestations associated with indicated group ID, wherein the space-timestreams for different stations are ordered based on the user positionfield of the group ID management frame.
 13. The non-transitorycomputer-readable storage medium of claim 12 wherein the one or moreprocessors are further configured to: establish a station-managementgroup to include two or more selected stations; configure the group IDmanagement frame to identify the selected stations in the membershipstatus field.
 14. The non-transitory computer-readable storage medium ofclaim 13 wherein the one or more processors are further configured togenerate a group update message comprising a group ID management frameto inform a station of its explicit deletion from the station-managementgroup.
 15. An apparatus of a communication station (STA) comprisinghardware processing circuitry and memory configured to: decode a groupID management frame that establishes group assignments for a multi-user(MU) multiple-input multiple-output (MIMO) (MU-MIMO) transmission, thegroup ID management frame comprising a membership status field and auser position field, the membership status field indicating groupmembership status of stations (STAs) for a plurality of group IDs, theuser position field indicating positions for the group IDs for STAsidentified as group members in the membership status field; determinemembership in a station-management group based on the membership statusfield of the group ID management frame; decode the MU-MIMO transmissionfor the stations indicated as being members in one of the groups, theMU-MIMO transmission comprising a group ID field indicating one of thegroup IDs and a multi-user field indicating a number of space-timestreams for the stations associated with the indicated group ID, whereinthe space-time streams for different stations are ordered based on theuser position field of the group ID management frame; and identify andprocess at least one of the space-time streams based on the multi-userfield when the group ID field indicates that the MU-MIMO transmission isintended for the station.
 16. The apparatus of claim 15 wherein thehardware processing circuitry is further configured perform interferencecancellation using one or more of the space-time steams of the MU-MIMOtransmission that are not intended for the station.
 17. The apparatus ofclaim 16 further comprising transceiver circuitry configured to receivea group update message comprising a group ID management frame to informthe STA of its explicit deletion from the station-management group. 18.The apparatus of claim 17 further comprising two or more antennascoupled to the transceiver circuitry.